Use of STAR-CCM+ in Marine and Off-Shore Engineering - Key Features and Future Developments - M. Perić, F. Schäfer, E. Schreck & J.

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1 Use of STAR-CCM+ in Marine and Off-Shore Engineering - Key Features and Future Developments - M. Perić, F. Schäfer, E. Schreck & J. Singh

2 Contents Main features of STAR-CCM+ relevant for marine and offshore applications Examples of industrial application New features under development

3 Important Features of STAR-CCM+ Easy process automation for maximum productivity High-resolution interface-capturing scheme for free surfaces (sharp interfaces, avoiding mixing) Different wave generation methods, wave theories, wave damping Cavitation modelling, user calibration Dynamic fluid-body interaction (6 DoF body motion), superposition of motions Overset grids for maximum flexibility in handling body motion Implicit fluid-structure interaction

4 Process Automation Unique features of STAR-CCM+ (pipeline-process, automatic meshing, reporting, monitoring, visualization ) make it possible to automate the simulation process The design of a suitable grid for a particular kind of vessel can be parameterized as a function of design features (length, width, waves etc.) This makes coupling to optimization tools easy (the optimization tool just replaces the geometry and re-runs the macro ). Process automation can be done by each user CDadapco also provides special tools to simplify the process (EHP, Simulation Assistant)

5 Interface-Capturing Scheme, I STAR-CCM+ uses an original High-Resolution Interface- Capturing (HRIC) scheme that produces sharp interfaces. Additional sharpening can be applied when grid or time step are not sufficient to keep the interface sharp (e.g. to prevent mixing in long-lasting sloshing simulations).

6 Interface-Capturing Scheme, II The user can still produce a smeared interface but that can usually be avoided Flow around a vertical cylinder two grids for the same initial free surface position: - Use mesh alignment to avoid unfavorable upstream conditions; - Use adequate time steps to maintain optimal HRIC-solution.

7 Waves In STAR-CCM+, one can simulate any means of wave generation (virtual experiment) Several wave theories are available (for initialization of solution, for boundary conditions, for comparison ). Superposition of many waves with different properties (including direction of propagation) is possible A wave damping method prevents reflections

8 Cavitation Modeling, I The homogeneous two-phase model is used, in which both phases are considered components of a single effective fluid. The equation for volume fraction of vapor has a source term which describes the growth and collapse of cavitation bubbles based on Rayleigh equation: Bubble radius Saturation pressure Local pressure Liquid density

9 Cavitation Modeling, II The model has two parameters: Seed bubbles, uniformly distributed in liquid (n 0 bubbles per unit volume of liquid); All seed bubbles have the same initial radius. Volume fraction of vapor in a control volume: The growth rate of bubble volume: The source term in equation for vapor volume fraction:

10 Cavitation Modeling, III A multiplier of the source term is provided for user to set up (default is 1.0): Either as a constant or field function; May be different for positive (bubble growth) and negative (bubble collapse) source term. This allows implementation of a new (user) cavitation model by making the multiplier such that the existing source term cancels out:

11 Superposition of Motions Superposition of vessel motion, propeller rotation, and oscillatory motion of each blade: easy set-up through GUI, no user programming needed...

12 Overset Grids, I Optimization of tidal turbine design using overset grids

13 Overset Grids, II Simulation of lifeboat launching using overset grids

14 Implicit Fluid-Structure Interaction Efficient simulation of fluid-structure interaction requires implicit coupling, i.e. updates of both flow-induced forces on the body and position and deformation of the body within every outer iteration. Solid body deformation with implicit coupling can be computed: - Within STAR-CCM+ using FVM (3D solids only); - Via co-simulation with ABAQUS. Coupling to other FEM-codes is also possible, but the exchange takes place once per time step.

15 Patrol Vessel, Validation Study, I Detailed simulation of flow, resistance, trim and sinkage were performed at the towing tank facility Brodarski Institut in Zagreb, Croatia

16 Patrol Vessel, Validation Study, II Experiments were performed in the towing tank of Brodarski Institut in Zagreb, Croatia, after simulations were finished. Resistance, trim and sinkage obtained in experiments agree well with simulation, both qualitatively and quantitatively, over the whole range of Froude numbers.

17 Off-Shore Application

18 America s Cup 2013, I ORACLE TEAM USA sailing in San Francisco Bay (America s Cup 2013) ORACLE TEAM USA sailing in a high-performance computer cluster (100 million cells, 256 cores; powered by STAR-CCM+, steered by Mario Caponnetto and his CFD analysis team)

19 America s Cup 2013, II ORACLE TEAM USA: The boat was designed and optimized solely by using simulation no model experiments done Simulations accompanied the race, guided changes to vessel (the night before the last race some modifications to rudder were done based on simulation results) and provided performance data to the crew

20 America s Cup 2013, III

21 STAR-CCM+: New Developments Additional motion models (prescribed in-plane motion + additional DoF) Virtual propeller model (using performance curves, theories or coupling to external solvers for propeller flow) Fluid-Structure-Interaction: Implementing FE-modelling into STAR-CCM+ (see presentation by Alan Mueller) Custom tool for an automatic set-up of standard tests: resistance, trim+sinkage (in future also PMM, circle, zig-zag ) Internal wave generation by mass source terms Coupling to other solvers (potential, Euler ) and theories Further developments of overset grids, automatic refinement Hydro-acoustics modelling, etc

22 New DFBI Motion Types, I New DFBI body motion options: - Four-DoF Maneuvering - Planar Motion Carriage Pure yaw Pure sway

23 New DFBI Motion Types, II Circle test

24 Virtual Propeller Model, I SVA Propeller Virtual Disk Momentum source terms are added to cells within a specified disk zone (grid does not have to be fitted to disk).

25 Virtual Propeller Model, II Full-scale hull, propeller and rudder, free surface, fixed hull Froude-number 0.21 Virtual Propeller With virtual propeller, free surface and hull resistance are well predicted with low cost Rotating Propeller

26 Internal Wave Generation Waves generated by mass sources/sinks (injection and suction of water) Waves reflected off a structure can pass through the internal wave generator Damping applied at all solution domain boundaries, except where reflection off walls is allowed

27 Coupling to Theory 3D solution coupled to wave theory (here: Stokes 5 th -order wave) over a zone along all vertical boundaries. This replaces both boundary conditions and damping Prevents reflection from inlet and side boundaries, as well as outlet Coupling zone Free surface

28 Future Trends More powerful and affordable computers = higher demands from simulation: More complete system analysis, with all geometrical details; More transient simulations (URANS, DES and LES), predicting pressure fluctuation and noise sources (turbulence, cavitation); More fluid-structure-interaction (slamming, sloshing) and other multi-physics (wind, fire, pollution etc.) applications; Simulation of manoeuvring tests (circle, zig-zag, PMM etc.) and other experiments in the design phase... Simulation of interaction (ship + ice, ship + platform, ship + ship etc.). More automatic optimization studies...